| 摘要 |
PURPOSE:To obtain an optical head device which has a position error of an optical spot smaller than the allowable value on an optical recording medium by using two specific prisms. CONSTITUTION:A semiconductor laser 1 is provided together with a collimator lens 2, the 1st and 2nd prisms 4 and 5, on objective lens 10, and a photodetector 22. The incident and refracted angles are referred to as PHI1 and theta1 on a 1st incident surface of a light beam with the incident and refracted angles referred to as PHI2 and theta2 on a 2nd incident surface respectively. Then the increments of the refraction rates of both prisms 4 and 5 are referred to as DELTAn1 and DELTAn2 respectively when the wavelength of the light beam increases by 1mm at a point near the center wavelength. Under such conditions, the conditions of an equation I are satisfied. As a result, the angle error value due to the change of the wavelength of the light beam is reduced in a prism radiation state. Then the position error of an optical spot can be reduced less than the allowable value on an optical recording medium 12. |
